How do I create four circular copies in edit mode?
Go to object mode, set the 3D cursor to the center of the shaft by selecting the shaft, hit CTRL + SHIFT + ALT + C and set origin at center of mass. Then, hit SHIFT + S and click cursor to selected. Now, go back to the blade, go in edit mode select everything. Set the Pivot point (button located next to 'Mode' and 'Material' buttons in the 3D view, and choose 3D cursor. Last, hit CTRL + D to duplicate, hit R and then the axis it should go around, type 90 and ENTER. Then keep hitting SHIFT + R to redo the that duplication until you have the right amount of blades.